Magnetic ion exchange resins have been used to remove various compounds from water supplies and waste streams. The resins are used to remove and concentrate a compound or compounds from a stream, and in some cases, move the compound into another stream. The term “compound” includes chemical compounds, elements and ions.
Ion exchange resins work by having functional groups incorporated within a polymer backbone which bind to compounds present within a solution to be treated. The functional groups can be selected so to provide binding sites suitable for binding to various types of compounds present within a solution. Weak acid cationic ion exchange resins are suitable for separating transition metal ions. Acidic organic materials, such as dissolved organic carbon (DOC) including humic and fulvic acids and other negatively charged ions, will bind to anion ion exchange resins. The binding effectiveness of the resin decreases as the compounds use up available binding sites on the resin. The spent resin is regenerated by applying a regenerate wash solution to the resin to reform the binding sites. Treatment with a regenerant solution produces a wash solution containing the separated compounds.
For ease of handling traditional ion exchange resins are contained within columns and the solution to be treated is pumped through the column. This restricts the types of processes in which the resin can be used.
Magnetic ion exchange resins are a significant improvement over traditional ion exchange resins. These resins have a discrete magnetic core or have magnetic particles dispersed throughout the resin. MIEX® brand resin from Orica Australia Pty Ltd is a macroporous ion-exchange resin having magnetic particles dispersed throughout the resin and is particularly suitable for use in removing DOC from potable water supplies. It has an advantage over other types of magnetic resins as all parts of the resin contain magnetic particles.
As described in U.S. Pat. No. 6,669,849, magnetic ion exchange resins can be used in the treatment of potable water supplies to remove DOC. It can be used as part of a multi-step treatment process and can provide a number of benefits in addition to the direct removal of DOC. For example, some water treatment processes employ activated carbon as a final polishing treatment to alleviate problems with taste and/or odour, to remove disinfection by-products or to remove any other pollutants. Pre-treatment with MIEX resin may also extend the effective life of the activated carbon.
Magnetic ion exchange resin can also be used in the treatment of waste streams. For example the Kraft process produces a highly coloured black effluent which is often released into water ways. Resin may be used to remove the colouring compounds from the effluent waste stream. Resin can also be used to remove and concentrate heavy metals from waste streams for additional processing.
A benefit of using magnetic ion exchange resins is that the weak magnetic properties of the resin allow the resin particles or beads to agglomerate together and quickly settle in settling tanks. This can facilitate the separation of resin from solution and thereby improve the methods of removing, recycling and regenerating resin. This has removed the need for columns to contain the resin and has permitted new treatment arrangements and methods for regenerating the resin, and continuous flow systems.
Processes for the use and separation of resins in the treatment of potable water are known and some have been described in U.S. Pat. No. 6,669,849. Magnetic ion exchange resins are described in U.S. Pat. Nos. 5,900,146 and 6,171,489. Other applications and patents relating to magnetic resins include International Application Nos. PCT/AU2005/001111, PCT/AU2005/000419, PCT/AU2004/000432, PCT/AU2005/000618, PCT/AU2005/001426 and U.S. application Ser. No. 11/124,624. The contents of these documents are incorporated by cross-reference.
There are a number of known methods for contacting and subsequently separating the magnetic ion exchange resins from a contacted liquid. The resin can be added to a contactor tank containing resin to which there is an inflow of raw water and an outflow of treatment water and resin. The resin may be dispersed by mechanical agitation such as stirrers and the like, mixing pumps immersed in the water or air agitation where a gas is bubbled through the water. Sufficient shear needs to be imparted on the water to achieve dispersal of the resin.
The resin then needs to be recovered from the water. The ion-exchange resin tends to be denser than the water and can settle to the bottom of the tank and can be separated by gravity settling. Alternatively the resin and water mixture can be pumped up through a separate resin settling tank. Such settling tanks are typically an upright elongate tank into which flows the stream of liquid and resin, the stream flows upward within the tank with the liquid being removed at the top. Resin agglomerates within the tank and gravity settled, and is then removed via an outlet located at or near the base of the tank.
U.S. Pat. No. 6,669,849 also describes a process for contacting and separating the ion-exchange resin from water flowing though a basin whereby the resin contacts the water in a first part of the basin and bulk of resin particles settle out in the first quarter of a separating basin length which is devoid of settler modules (“free-flowing” settling). Further removal of resin particles (“enhanced” settling) from treated water is performed in a settler compartment filled with modules which may be either tilted plates or tubular modules. The bottom of the settler is designed for collection of resin particles in cylindrical, conical or pyramidal hoppers from which the resin particles are pumped back to the contactor region.
Basin systems or separate contactor and separator tanks require a large amount of space and can significantly increase the capital cost of using a magnetic ion exchange resin process.
Another option is to confine the resin within a localised region. U.S. Pat. No. 5,230,805 (Yates et al) describes a system of magnetically stabilised fluidised particles within liquid media. Fluidised magnetic resin within an upwardly flowing liquid stream is stabilised and held within a general area by the application of a magnetic field of 25 to 500 gauss, preferably by an electromagnet that encircles the treatment area. This arrangement requires the ongoing application of a strong magnetic field to retain the resin beads within a contact region and it is unlikely that the resin could be economically retained within the region at moderate to high liquid upflow rates.